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Abstract:

A phase shifter is provided. The phase shifter includes a first phase
shifter that is continuously adjustable within a range of 0 degrees to 90
degrees, two 4-way switches each configured to selectively switch on one
of a capacitance, an inductance, an open circuit, and a short circuit
under control of a control voltage, and a bridge. A first input end and a
first output end of said bridge are respectively connected to a first
4-way switch of the two 4-way switches. A second input end of said bridge
is connected to an output end of said first phase shifter or a second
output end of said bridge is connected to an input end of said first
phase shifter.

Claims:

1. A phase shifter comprising: a first phase shifter that is continuously
adjustable within a range of 0 degrees to 90 degrees; two 4-way switches
each configured to selectively switch on one of a capacitance, an
inductance, an open circuit, and a short circuit under control of a
control voltage; and a bridge, wherein: a first input end and a first
output end of said bridge are respectively connected to a first 4-way
switch of the two 4-way switches; and one of a second input end of said
bridge is connected to an output end of said first phase shifter and a
second output end of said bridge is connected to an input end of said
first phase shifter.

2. A phase shifter according to claim 1, wherein said control voltage is
one of 00, 01, 10, 11 in binary form.

3. A phase shifter according to claim 1, wherein said two 4-way switches
select the capacitance and the inductance depending on a working
frequency.

4. A phase shifter according to claim 1, wherein said first phase shifter
comprises: a bridge and two varactors, wherein the two varactors are
respectively connected to two power dividing ports of the bridge; an
input port connected to an input end of the bridge; an output port
connected to an isolation port of the bridge; and a plurality of
resistances configured to provide current protection and voltage bias for
the two varactors.

5. A power amplifier comprising a phase shifter comprising: a first phase
shifter that is continuously adjustable within a range of 0 degrees to 90
degrees; two 4-way switches each configured to selectively switch on one
of a capacitance, an inductance, an open circuit, and a short circuit
under control of a control voltage; and a bridge, wherein: a first input
end and a first output end of said bridge are respectively connected to a
first 4-way switch of the two 4-way switches; and one of a second input
end of said bridge is connected to an output end of said first phase
shifter and a second output end of the bridge is connected to an input
end of said first phase shifter.

6. A power amplifier according to claim 5, wherein the control voltage is
one of 00, 01, 10, 11 in binary form.

7. A power amplifier according to claim 5, wherein the two 4-way switches
select the capacitance and the inductance depending on a working
frequency.

8. A power amplifier according to claim 5, wherein said first phase
shifter comprises: a bridge and two varactors, wherein the two varactors
are respectively connected to two power dividing ports of the bridge; an
input port connected to an input end of the bridge; an output port
connected to an isolation port of the bridge; and a plurality of
resistance configured to provide current protection and voltage bias for
the two varactors.

9. A magnetic resonance imaging apparatus comprising a power amplifier
comprising a phase shifter comprising: a first phase shifter that is
continuously adjustable within a range of 0 degrees to 90 degrees; two
4-way switches each configured to selectively switch on one of a
capacitance, an inductance, an open circuit, and a short circuit under
control of a control voltage; and a bridge, wherein: a first input end
and a first output end of said bridge are respectively connected to a
first 4-way switch of the two 4-way switches; and one of a second input
end of said bridge is connected to an output end of said first phase
shifter and a second output end of the bridge is connected to an input
end of said first phase shifter.

10. A magnetic resonance imaging apparatus in accordance with claim 9,
wherein the control voltage is one of 00, 01, 10, 11 in binary form.

11. A magnetic resonance imaging apparatus in accordance with claim 9,
wherein the two 4-way switches select the capacitance and the inductance
depending on a working frequency.

12. A magnetic resonance imaging apparatus in accordance with claim 9,
wherein said first phase shifter comprises: a bridge and two varactors,
wherein the two varactors are respectively connected to two power
dividing ports of the bridge; an input port connected to an input end of
the bridge; an output port connected to an isolation port of the bridge;
and a plurality of resistance configured to provide current protection
and voltage bias for the two varactors.

13. A phase shifter according to claim 1, wherein the two 4-way switches
are configured to generate a phase shift of 0 degrees when the two 4-way
switches switch the capacitance on.

14. A phase shifter according to claim 1, wherein the two 4-way switches
are configured to generate a phase shift of 90 degrees when the two 4-way
switches switch the open circuit on.

15. A phase shifter according to claim 1, wherein the two 4-way switches
are configured to generate a phase shift of 180 degrees when the two
4-way switches switch the inductance on.

16. A phase shifter according to claim 1, wherein the two 4-way switches
are configured to generate a phase shift of 270 degrees when the two
4-way switches switch the short circuit on.

17. A power amplifier according to claim 5, wherein the two 4-way
switches are configured to generate a phase shift of 0 degrees when the
two 4-way switches switch the capacitance on.

18. A power amplifier according to claim 5, wherein the two 4-way
switches are configured to generate a phase shift of 90 degrees when the
two 4-way switches switch the open circuit on.

19. A power amplifier according to claim 5, wherein the two 4-way
switches are configured to generate a phase shift of 180 degrees when the
two 4-way switches switch the inductance on.

20. A power amplifier according to claim 5, wherein the two 4-way
switches are configured to generate a phase shift of 270 degrees when the
two 4-way switches switch the short circuit on.

Description:

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of Chinese Patent Application
No. 201010193734.8 filed May 31, 2010, which is hereby incorporated by
reference in its entirety.

BACKGROUND OF THE INVENTION

[0002] The present invention generally relates to very low frequency
field, and especially relates to a phase shifter and power amplifier and
magnetic resonance imaging apparatus in the nuclear magnetic resonance
imaging technology.

[0003] The nuclear magnetic resonance imaging technology is applied
broadly in the medical field at present. The magnetic resonance imaging
(MRI) is also called nuclear magnetic resonance imaging (NMRI), which is
a diagnostic method that generates an image by atomic nucleus resonance
in the magnetic field. The basic principle is forming an image by
utilizing the inherent characteristics of atomic nucleus and the
interaction of a magnetic field. A type of atomic nucleus closely related
to tissues of the human body generates magnetic resonance signals under
the effect of an external radio frequency field. A set of parameters
related to the magnetic resonance may serve as imaging variables. A power
amplifier is one of the components within a magnetic resonance imaging
apparatus.

[0004] As is known, power amplifier linearity technology, for example,
feedback, feed forward and predistortion, etc., is the mainstream in
enhancing the Adjacent Channel Power Ratio (ACPR) and improving the power
amplifier linearity. This technology compares the amplitude and phase of
the input signal and the output signal, thus, the phase shift function of
a phase shifter is employed.

[0005] A known current phase shifter is shown in FIG. 1. In the current
phase shifter, capacitance C1 and C2 are connected in series between an
input port Pin and an output port Pout. A diode 8 and a diode 9 connected
in parallel are grounded at one end and are connected to a capacitance C3
at the other end. The other end of the capacitance C3 is connected to an
inductance L. The other end of the inductance L is connected between the
capacitance C1 and C2. A control voltage is applied between the
capacitance C3 and the diodes 8, 9 connected in parallel via a resistance
R1. For example, the input port Pin and the output port Pout are ports
with 50 Ohm, where the working frequency is about 64 Mhz, the
capacitances C1, C2 and C3 are approximately 3.3 nF, the inductance L is
about 47 nH, and the resistance R1 is about 1 k Ohm. Other values may be
possible. As shown in FIG. 1, the impedance of the diode 8 and diode 9
will vary with the changes of the bias voltage. The changes of the
impedances of the diode 8 and diode 9 inevitably cause phase variation
from the output port Pout to the input port Pin, thereby achieving the
purpose of phase shift. However, the changes of the phase shift caused by
this example is about 26 degrees, thus the range of phase shift is too
small, while the insertion loss is rather large, which influences system
gain and noise.

[0006] Another known current phase shift is shown in FIG. 2. An input port
Pin is connected to an input end of a bridge 3, and an output port Pout
is connected to an isolation port of the bridge 3. The anodes of two
varactors 4 and 5 are respectively connected to two power dividing ports
of the bridge 3. The two power dividing ports are also respectively
connected to grounding resistance R2 and R5. The cathodes of the two
varactors 4 and 5 are respectively connected to resistance R3 and R4 and
are connected in series with a control voltage. A capacitance C4 is
connected to control voltage at one end, and is grounded at the other
end. Resistances R2, R3, R4, R5 provide current protection and voltage
bias for the two varactors, and the capacitance C4 performs the function
of blocking and filtering. This type of phase shift technology is very
popular and may be applied to many fields, especially in mobile
communication and radar fields. In this example, it is assumed that the
input port Pin and the output port Pout are ports with 50 Ohm. It can be
seen from FIG. 2 that the reactances of the varactor 4 and varactor 5
vary with the variation of the control voltage, so the phase variation of
the emitted signals will be different, and thus a phase delay is
realized.

[0007] Compared to the phase shifter shown in FIG. 1, the phase shifter
shown in FIG. 2 shifts phase in a broader range, however, it is difficult
to realize a phase shift of 180 degrees.

SUMMARY OF THE INVENTION

[0008] The embodiments described herein provide a phase shifter and power
amplifier and magnetic resonance imaging apparatus by which a phase shift
range of 0 degrees to 360 degrees can be realized.

[0009] More specifically, the phase shifter described herein includes a
first phase shifter continuously adjustable within the range of 0 degrees
to 90 degrees. The phase shifter includes a bridge and two 4-way
switches. An input end and an output end of the bridge are respectively
connected to one 4-way switch. The two 4-way switches are designed to
selectively switch on one of a capacitance, an inductance, an open
circuit, and a short circuit under the control of a control voltage.
Another input end of the bridge is connected to an output end of the
first phase shifter, or another output end of the bridge is connected to
an input end of the first phase shifter.

[0010] The control voltage is one of 00, 01, 10, 11 in binary form.

[0011] The selection of the capacitance and the inductance is dependent on
a working frequency.

[0012] The first phase shifter includes a bridge and two varactors, an
input port connected to an input end of the bridge, and an output port
connected to an isolation port of the bridge. The two varactors are
respectively connected to two power dividing ports of the bridge.
Resistances R2, R3, R4, R5 provide current protection and voltage bias
for the two varactors

[0013] In another aspect, the power amplifier of the includes a phase
shifter, and the phase shifter includes a first phase filter that is
continuously adjustable within the range of 0 degrees to 90 degrees. The
phase shifter further includes a bridge and two 4-way switches. An input
end and an output end of the bridge are respectively connected to one
4-way switch. The two 4-way switches are designed to selectively switch
on one of a capacitance, an inductance, an open circuit, and a short
circuit under the control of a control voltage. Another input end of the
bridge is connected to an output end of the first phase shifter, or
another output end of the bridge is connected to an input end of the
first phase shifter.

[0014] The control voltage is one of 00, 01, 10, 11 in binary form.

[0015] The selection of the capacitance and the inductance is dependent on
a working frequency.

[0016] The first phase shifter includes a bridge and two varactors, an
input port connected to an input end of the bridge, and an output port
connected to an isolation end of the bridge. The two varactors are
respectively connected to two power dividing ports of the bridge.
Resistances R2, R3, R4, R5 provide current protection and voltage bias
for the two varactors.

[0017] Correspondingly, the magnetic resonance imaging apparatus includes
the power amplifier described above.

[0018] Compared with known phase shifters, the phase shifter and power
amplifier and magnetic resonance imaging apparatus described herein have
the following advantageous effects.

[0019] First, because the embodiments described herein include two 4-way
switches and a bridge, when the two 4-way switches are selected to switch
on the capacitance, a phase shift of 0 degrees is generated. When the two
4-way switches are selected to switch on the open circuit, a phase shift
of 90 degrees is generated. When the two 4-way switches are selected to
switch on the inductance, a phase shift of 180 degrees is generated. When
the two 4-way switches are selected to switch on the short circuit (i.e.
grounding), a phase shift of 270 degrees is generated. Moreover, a first
phase shifter is continuously adjustable in shifting a phase from 0
degrees to 90 degrees, thus a phase shift that is continuously adjustable
from 0 degrees to 360 degrees can be realized.

[0020] Second, because this type of phase shifter has little insertion
loss, the matching of standing waves of the input and output ports are
nice. This type of phase shifter is very important for a high power
amplifier, as it not only can reduce power loss, but also can avoid
self-excitation of power amplifier. Further, the phase shifter is easy to
control and is convenient to use.

BRIEF DESCRIPTION OF THE DRAWINGS

[0021] For a thorough understanding of the present disclosure, reference
will be made to the description in combination with the figures, in
which:

[0022]FIG. 1 is a structural schematic diagram of a phase shifter of the
prior art;

[0023]FIG. 2 is a structural schematic diagram of another phase shifter
of the prior art;

[0024]FIG. 3 is a schematic diagram of a phase shifter in accordance with
the present invention.

DETAILED DESCRIPTION OF THE INVENTION

[0025] The embodiments of the present invention will be described in
detail as follows, however, the present invention is not limited to the
following embodiments.

[0026] As shown in FIG. 3, the phase shifter includes a first phase
shifter 1 that is continuously adjustable within a range of 0 degrees to
90 degrees, a bridge 13, and two 4-way switches 14 and 14'. An input end
of the bridge 13 is connected to the 4-way switch 14, and an output end
of the bridge 13 is connected to the 4-way switch 14'. The 4-way switch
14 is designed to selectively switch on one of a capacitance C, an
inductance L, an open circuit, and a short circuit under the control of
control voltages B and C. The 4-way switch 14' is designed to selectively
switch on one of a capacitance C', an inductance L', an open circuit, and
a short circuit under the control of control voltages B and C. Another
input end 11 of the bridge 13 is connected to an output end of the first
phase shifter 1. Another output end of the bridge 13 may be connected to
an input end of the first phase shifter 1.

[0027] As seen from the above, the 4-way switches 14 and 14' respectively
have four selections and may be controlled by control voltages B and C.
When the 4-way switch 14 is selected to switch on the capacitance C and
the 4-way switch 14' is selected to switch on the capacitance C', the
phase variation between the input end 11 and the output end 12 of the
bridge 13 is 0 degrees, i.e., there is no phase shift. When the 4-way
switches 14 and 14' are both selected to be open circuit, the phase
variation between the input end 11 and the output end 12 of the bridge 13
is 90 degrees, i.e., the phase shift is 90 degrees. When the 4-way switch
14 is selected to switch on the inductance L and the 4-way switch 14' is
selected to switch on the inductance L', the phase variation between the
input end 11 and the output end 12 of the bridge 13 is 180 degrees, i.e.,
the phase shift is 180 degrees. When the 4-way switches 14 and 14' are
both selected to switch on short circuit (i.e. grounding), the phase
variation between the input end 11 and the output end 12 of the bridge 13
is 270 degrees, i.e., the phase shift is 270 degrees.

[0028] Thus, phase shift of 0 degrees, 90 degrees, 180 degrees, and 270
degrees can be realized by the structure of the bridge 13 and the two
4-way switches 14 and 14'.

[0029] Again, as shown in FIG. 1, the first phase shifter 1 is a phase
shifter the is continuously adjustable from 0 degrees and 90 degrees.
More specifically, the phase shift range of the first phase shifter 1 is
from 0 degrees and 90 degrees. In other words, the first phase shifter 1
can shift phase to any degree from 0 degrees to 90 degrees.

[0030] If the input end of the first phase shifter 1 is made as the input
port of the phase shifter, the output end of the first phase shifter 1 is
connected to the input end 11 of the bridge 13, and if the output end 12
of the bridge 13 is made as the output port of the phase shifter of the
present invention, the phase difference between the input port and the
output port may be at four phase regions: 0 degrees-90 degrees; 90
degrees-180 degrees; 180 degrees-270 degrees; 270 degrees-360 degrees. In
other words, the phase difference between the input port and the output
port may be any value from 0 degrees to 360 degrees. Thus, a continuously
adjustable phase shift from 0 degrees to 360 degrees is realized.

[0031] As for control voltages B and C, they only need to control the
4-way switches 14 and 14' to make a selection. For example, they may be
binary 00, 01, 10, 11, respectively for controlling the 4-way switches 14
and 14' to selectively switch on one of the capacitance (C, C'),
inductance (L, L'), open circuit and short circuit.

[0032] The selection for the capacitance C, C' and inductance L, L' is
dependent on the working frequency.

[0033] For example, assuming that the working frequency is 64 MHz, a
capacitance of about 50 pF should be selected for the capacitance C and
C', and an inductance of about 125 nH should be selected for the
inductance L and L'. Radio frequency switches should be selected as the
two 4-way switches 14 and 14', and a 3 dB bridge should be selected as
the bridge 13. Thus, when the two 4-way switches 14 and 14' are selected
to switch on the capacitance C and C', or to switch on the inductance L
and L', a phase variation of 0 degrees and 180 degrees may be
respectively generated between the input port and the output port, and
the insertion loss is about 0 dB, as shown in Table 1 as follows.

Wherein, "1.000" in X represents the first item of simulation, dB(S(2,1))
represents the insertion loss or gain between the output and input ports,
Phase(S(2,1)) represents the phase difference between the output and
input ports, the frequency is 64 MHZ. This is the result of selecting a
50 PF capacitance by the switch.

In the table 2, the result of selecting a 125 nH inductance by the switch
is presented.

[0034] Any phase shifter that is continuously adjustable from 0 degrees to
90 degrees may be used as the first phase shifter 1. The phase shifter
shown in FIG. 2 may serve as the first phase shifter 1.

[0035] Further, a power amplifier includes a phase shifter. The phase
shifter includes a phase shifter 1 that is continuously adjustable within
a range of 0 degrees to 90 degrees. The phase shifter further includes a
bridge 13 and two 4-way switches 14 and 14'. An input end and an output
end of the bridge 13 are respectively connected to one 4-way switch. An
input end of the bridge 13 is connected to the 4-way switch 14, and an
output end of the bridge 13 is connected to the 4-way switch 14'. The
4-way switch 14 is designed to selectively switch on one of a capacitance
C, an inductance L, an open circuit, and a short circuit under the
control of control voltages B and C. The 4-way switch 14' is designed to
selectively switch on one of a capacitance C', an inductance L', an open
circuit, and a short circuit under the control of control voltages B and
C. Another input end 11 of the bridge 13 is connected to an output end of
the first phase shifter 1. Another output end of the bridge 13 may be
connected to an input end of the first phase shifter 1.

[0036] As seen from the above, the 4-way switches 14 and 14' respectively
have four selections and may be controlled by control voltages B and C.
When the 4-way switch 14 is selected to switch on the capacitance C and
the 4-way switch 14' is selected to switch on the capacitance C', the
phase variation between the input end 11 and the output end 12 of the
bridge 13 is 0 degrees, i.e., there is no phase shift. When the 4-way
switches 14 and 14' are both selected to be open circuit, the phase
variation between the input end 11 and the output end 12 of the bridge 13
is 90 degrees, i.e., the phase shift is 90 degrees. When the 4-way switch
14 is selected to switch on the inductance L and the 4-way switch 14' is
selected to switch on the inductance L', the phase variation between the
input end 11 and the output end 12 of the bridge 13 is 180 degrees, i.e.,
the phase shift is 180 degrees. When the 4-way switches 14 and 14' are
both selected to switch on short circuit (i.e. grounding), the phase
variation between the input end 11 and the output end 12 of the bridge 13
is 270 degrees, i.e., the phase shift is 270 degrees.

[0037] Thus, phase shift of 0 degrees, 90 degrees, 180 degrees, and 270
degrees can be realized by the structure of the bridge 13 and the two
4-way switches 14 and 14'.

[0038] Again, as shown in FIG. 1, the first phase shifter 1 is a phase
shifter that is continuously adjustable from 0 degrees and 90 degrees.
More specifically, the phase shift range of the first phase shifter 1 is
from 0 degrees and 90 degrees. In other words, the phase shifter 1 can
shift phase to any angle from 0 degrees to 90 degrees.

[0039] If the input end of the first phase shifter 1 is made as the input
port of the phase shifter, the output end of the first phase shifter 1 is
connected to the input end 11 of the bridge 13, and is the output end 12
of the bridge 13 is made as the output port of the phase shifter, the
phase difference between the input port and the output port may be at
four phase regions: 0 degrees-90 degrees; 90 degrees-180 degrees; 180
degrees-270 degrees; 270 degrees-360 degrees. That is, the phase
difference between the input port and the output port may be any value
from 0 degrees to 360 degrees. Thus, a continuously adjustable phase
shift from 0 degrees to 360 degrees is realized.

[0040] As for control voltages B and C, they only need to control the
4-way switches 14 and 14' to make a selection. For example, they may be
binary 00, 01, 10, 11, respectively for controlling the 4-way switches 14
and 14' to switch on one of the capacitance (C, C'), inductance (L, L'),
open circuit and short circuit.

[0041] The selection for the capacitance C, C' and inductance L, L' is
dependent on the working frequency.

[0042] Because the power amplifier includes the phase shifter that is
continuously adjustable from 0 degrees to 360 degrees as described above,
the linearity of the power amplifier described herein is very nice.
Moreover, signals will not be distorted and the power may be even
greater.

[0043] In another aspect, a magnetic resonance imaging apparatus is
provided. The magnetic resonance imaging apparatus includes the power
amplifier described above. Since the power amplifier has been described
in detail in the text above, here we will not go further on it.

[0044] Although the embodiments of the present invention have been
described in combination with the figures in the text above, yet those
skilled in the art may make various variation, modification and
equivalence on the present invention without departing from the spirit
and scope of the present invention. These variation, modification and
equivalence are intended to fall within the spirit and scope defined by
the appended claims.